A wear resistance-requiring mechanical component, e.g., a tappet, has been widely used for the purpose of opening and closing a suction valve and an exhaust valve of an engine. The tappet comes into contact with a cam surface at its bottom side so as to convert a rotational movement of a cam shaft into a vertical movement thereof, thus opening and closing the valves via a rocker arm. The conventional tappet comprises a metal body and a wear resistant tip, the latter of which is provided with a crown-shaped sliding surface whose middle section is higher than its periphery by several to several tens micrometers. This wear resistant tip, for example, is made of silicon nitride, silicon carbide, sialon or cemented carbide and can be brazed to the metal body.
There are two ways of making the crown-shaped sliding surface of the wear resistant tip. One way is to sinter the wear resistant tip and then to grind the sintered wear resistant tip into the crown shape, which costs too much because the crown-shaped surface is a tertiary curved surface. The other way is to give the crown shape to a ceramic in advance of sintering and then to sinter it into the wear resistant tip. This way, however, tends to deteriorate dimensional precision of the wear resistant tip due to contraction of the tip during the sintering process.
As a solution to the above-stated problems, Japanese Patent Publication No. 6-74811 discloses a method of producing a sliding part in which a wear resistant member having a smaller coefficient of thermal expansion than that of the metal body is thermally brazed to the sliding surface so that the opposite surface of the wear resistant member from the brazed surface is deformed into the crown shape owing to the difference in the coefficient of thermal expansion.
Nevertheless, the method disclosed in the Japanese publication still has a problem in that the crown value becomes too high when the brazed surface between the metal body and the wear resistant member is vast or when the difference between their coefficients of thermal expansion is large. This problem is remarkable in case of brazing steel and silicon nitride(Si.sub.3 N.sub.4) whose coefficients of thermal expansion are 13.times.10.sup.-6 /.degree.C. and 3.2.times.10.sup.-6 /.degree.C., respectively. If the crown value is exceedingly great as stated above, not only the periphery of the wear resistant member is apt to be cracked due to the increased residual stress, but also the stress is concentrated in the middle section of the wear resistant member, thus resulting in the fracture of the wear resistant member. If the crown value is too small to the contrary, the sliding surface becomes so flat that a desired shape of the wear resistant mechanical component cannot be achieved. In a nutshell, the Japanese publication does not disclose a method whereby the crown value of the wear resistant member is precisely controlled, but teaches a method of merely deforming the wear resistant member into the crown shape.